In recent years, in the treatment of disease, such as renal disease with serious complications of the circulatory system, and multiple organ failure, blood purification, collectively called continuous blood purification, has become common and achieved clinical effects, particularly in the area of emergency and intensive care.
Continuous blood purification specifically includes continuous hemofiltration (hereinafter referred to as “CHF”), continuous hemodialysis (hereinafter referred to as “CHD”), continuous hemodiafiltration (hereinafter referred to as “CHDF”), and the like and is appropriately used according to the purpose of treatment.
Here, CHF is a method in which blood is flowed into a blood purifier that houses a semipermeable membrane to drain filtrate containing waste products from the blood through the filtration membrane, while supplying a replacement fluid into the body, and the entire process is performed continuously and slowly. Similarly, CHD is a method for continuously and slowly performing the correction of acid-base equilibrium, and the like by diffusion through a semipermeable membrane. CHDF is a combined method of the CHF and the CHD in which to improve the small molecular weight removal ability of the CHF, a dialysate is flowed on the filtrate side so as to obtain the effect of dialysis as well.
Also, as blood purification for liver failure, apheresis, or plasma exchange (hereinafter referred to as “PE”), is selected depending on the purpose of treatment and achieves clinical effects.
Here, PE is a method for removing hazardous substances metabolized and detoxified by the liver and supplying useful substances synthesized by the liver.
In any blood purification of CHF, CHD, and CHDF, as also called “continuous and slow,” blood purification is performed usually in a gradual manner over several days for one treatment, which is the feature of this treatment, and this treatment is greatly different in a time scale from simple hemodialysis and hemofiltration in which one treatment time is 4 to 5 hours.
As a first preferred example of a blood purification apparatus using the continuous blood purification, Patent Document 1 (Japanese Patent Application Laid-Open No. 9-239024) describes a blood purification system comprising at least either of dialysate supplying means for hemodialysis and replacement fluid supplying means for hemofiltration, drainage means, and a blood circulation path, wherein the means respectively comprise storage containers, feed pumps, and a plurality of scales for measuring the storage containers, and wherein the flow rate of each feed pump is individually controlled, based on information from each scale.
FIG. 25 is a conceptual view showing the blood purification system using continuous blood purification in the first example described above. This blood purification system is composed of a blood drawing tubing part 81 and a blood returning tubing part 82 which constitute a blood circulation path, a drainage flow path 12 which drains water containing waste products, a replacement fluid flow path 54 connected to the blood returning tubing part 82 to inject a replacement fluid into a patient, and a dialysate flow path 35 which supplies a dialysate to the filtrate side in a blood purifier 91. A blood pump 71 is located in the blood drawing tubing part 81, and the blood purifier 91 housing a filtration membrane 92 is located between the blood drawing tubing part 81 and the blood returning tubing part 82.
The drainage flow path 12 comprises a drainage feed pump 101 which drains a filtrate and a dialysis drainage from the blood purifier 91, a drainage storage container 141 connected to a drainage flow path 17 branching off on the outlet side of the drainage feed pump 101, and a drainage blocking valve 111 attached to a drainage flow path 13 on the downstream side of the branch part. Also, a scale for drainage measurement 151 is provided on the drainage storage container 141.
The dialysate flow path 35 comprises a feed pump 102 for a dialysate which supplies the dialysate to the filtrate side in the blood purifier 91, a dialysate storage container 142 connected to a dialysate flow path 37 branching off on the inlet side of the dialysate feed pump 102, and a dialysate supply blocking valve 112 attached to a dialysate flow path 32 on the upstream side of the branch part. A scale for dialysate measurement 152 is provided on the dialysate storage container 142.
The replacement fluid flow path 54 comprises a replacement fluid feed pump 103 which supplies the replacement fluid to the patient, a replacement fluid storage container 143 connected to a replacement fluid flow path 57 branching off on the inlet side of the replacement fluid feed pump 103, and a replacement fluid supply blocking valve 113 attached to a replacement fluid flow path 52 on the upstream side of the branch part. A scale for replacement fluid measurement 153 is provided on the replacement fluid storage container 143.
Blood taken out of the patient by the blood pump 71 passes through the blood drawing tubing part 81 and is introduced into the blood purifier 91 in which the filtration membrane 92 is housed, and waste products and the like are removed. In the blood purifier 91, the dialysate is supplied by the dialysate feed pump 102 for acid-base equilibrium and the like, and the filtrate and the dialysis drainage are drained by the drainage feed pump 101. When the blood subjected to filtration and dialysis in the blood purifier 91 is returned to the patient through the blood returning tubing part 82, the replacement fluid is added to the blood by the replacement fluid feed pump 103, and the blood is injected into the patient.
This system is advantageous in that treatment can be safely continued while the amount of the body fluid of the patient is suitably controlled without requiring frequent measurement and adjustment operations by a staff. Further, this system is advantageous in that the replacement of a dialysate storage part 121 and a replacement fluid storage part 122, and the replacement of a tank in the case where the filtrate and the dialysis drainage are stored in the tank or the like, can be performed at any time without directly affecting the measurement of the amount of water removed and without stopping treatment.
The feed pump has some feed error. To reduce the effect of the error as much as possible, in the above system, the scales 151, 152, and 153 are located on the storage containers 141, 142, and 143 respectively, and data from the scales are fed to a controller not shown. The controller constantly monitors the data of the scales 151, 152, and 153 and calculates an actual flow rate from a change in weight per unit time. When there is a difference between the actual flow rate and a set flow rate, the number of revolutions of motors for the feed pumps 101, 102, and 103 is individually automatically adjusted, and controlled so that the set flow rate and the actual flow rate are equal, thereby maintaining flow rate precision.
The above-described system can maintain high flow rate precision, but due to factors, such as the temperature characteristics of the weight sensor and the electronic circuit for measurement, change over time, the method of adjustment used during manufacture, and a change in the shape of each storage container, it is inevitable that each feed pump has flow rate precision with an error of about 1% in actual operation.
As described above, the amount of water removed for a patient with renal failure is controlled as an important parameter, and the amount of water removed ΔV (L) is obtained by the following formula (1).ΔV=VF−VC−VD  (1)
In the formula (1), VF (L) is the amount of the drainage drained by the drainage feed pump 101, VC (L) is the amount of the replacement fluid supplied by the replacement fluid feed pump 103, and VD (L) is the amount of the dialysate supplied by the dialysate feed pump 102.
Conventionally, in performing the treatment of the CHDF, the feed pump is generally used at a flow rate of about 1 L/h. For example, when the flow rate of the drainage feed pump 101 is set at 1 L/h, the flow rate of the replacement fluid feed pump 103 is set at 0.5 L/h, and the flow rate of the dialysate feed pump 102 is set at 0.5 L/h, and when the flow rate error of each feed pump is about 1%, VF=24±0.24 (L), VC=12±0.12 (L), and VD=12±0.12 (L) are provided in 24 hours. When the amount of water removed ΔV is calculated, based on the formula (1), ΔV=0±0.48 (L) is provided, so that the error of water removed can be reduced to about 0.48 (L), corresponding to 2% of the amount of the drainage VF, or less. This theory also applies to systems shown in Patent Document 2 (Japanese Patent No. 3180309) and Patent Document 3 (Japanese Patent No. 3413412), in which the flow rate error of each pump is also about 1%.
On the other hand, in recent years, in performing the treatment of CHDF or the like, the case where the treatment is performed with a high flow rate of the feed pump, to perform the treatment more efficiently, has been increasing. In this case, with a system in which the flow rate error of each feed pump is about 1% as in a conventional system, for example, when the flow rate of the drainage feed pump 101 is set at 5 L/h, the flow rate of the replacement fluid feed pump 103 is set at 2.5 L/h, and the flow rate of the dialysate feed pump 102 is set at 2.5 L/h, and when the flow rate error of each feed pump is about 1%, VF=120±1.2 (L), VC=60±0.6 (L), and VD=60±0.6 (L) are provided in 24 hours. When the amount of water removed ΔV is calculated, based on the formula (1), ΔV=0±2.4 (L) is provided, so that the error of water removed is as much as about 2.4 L, corresponding to 2% of the amount of the drainage VF.
With such a large error, a problem may be that a risk that the balance of the body fluid of the patient is abnormal is greater than the treatment effect of blood purification. To solve this problem, as a second example, a system in Patent Document 4 (Japanese Patent No. 3714947) comprises dialysate supplying means for hemodialysis, replacement fluid supplying means for hemofiltration, drainage means, and a blood circulation path, wherein the means respectively comprise storage containers and feed pumps, and comprise one scale for simultaneously measuring the three storage containers. The blood purification system wherein the flow rate of each feed pump is individually controlled, based on information from this scale is described.
FIG. 26 is a conceptual view showing the blood purification system using continuous blood purification in the second example described above. In this blood purification system, a scale 154 which simultaneously measures three storage containers, a drainage storage container 141, a dialysate storage container 142, and a replacement fluid storage container 143, is provided. It is reported that the error of water removed is reduced to about 0.5% of VF because the amount of water removed ΔV in the formula (1) is measured by the scale 154.
In the area of emergency medical care and intensive care, the treatment of CHDF and the like has become general, and the case where the treatment is performed with the flow rate of the feed pump being a high flow rate of about 10 L/h, to perform the treatment more efficiently, also has been increasing. The system in Patent Document 4 has a great feature that the error of water removed can be reduced. However, since the system configuration is complicated, further improvement has been required. To mount in the apparatus the blood tubing branching off in a complicated manner, complicated operations are necessary, and particularly, the operator is required to reliably mount a portion associated with the storage container because it directly affects the result of measurement. However, any of a drainage flow path 17, a dialysate flow path 37, and a replacement fluid flow path 57 connected to the measurement container is mounted twisted, pulled, or with the ducts crossed, or the like, so that measurement may be affected.    Patent Document 1: Japanese Patent Application Laid-Open No. 9-239024    Patent Document 2: Japanese Patent No. 3180309    Patent Document 3: Japanese Patent No. 3413412    Patent Document 4: Japanese Patent No. 3714947